This invention relates generally to mobile telecommunication systems, and more particularly, to extending the existing GPRS architectural model to include multi-beam geostationary satellite systems. Disclosed are a method and apparatus providing an efficient solution to the problem of least cost routing for packet data traffic to/from IP networks in a mobile satellite system employing General Packet Radio Service (GPRS) network infrastructure.
General Packet Radio Service (GPRS) is a random access packet data extension (data service) of the Global System for Mobile communications (GSM). GPRS uses a packet-mode technique to transfer high and low speed data and signaling in an efficient manner. The GPRS network infrastructure is built into the existing GSM system architecture with additional network elements, interfaces and identities. GPRS is composed of both radio access and network subsystems.
The GSM and GPRS standards are defined in technical specifications published by the European Telecommunications Standards institute (ETSI). These include ETSI GSM 03.03, ETSI GSM 03.60 and ETSI GSM 09.60, which are herein incorporated by reference.
A detailed description of the GPRS logical network architecture, Mobility & Location Management and Packet Routing Procedures can be found in the ETSI GSM Specification 03.60.
Basically, GPRS radio channels allocated flexibly in a TDMA frame, and the timeslots are shared by the active users. Uplink and downlink channels are allocated separately, and the radio interface resources may be shared dynamically between speech and data services based on, for example, load and operator preference. A variety of channel coding schemes are defined in the specification to provide a diversity of bit rates from 9 to more than 150 kbit/s per user. Generally, applications based on standard data protocols are supported, and interworking is defined with both IP networks and X.25. Network interworking is required whenever a network supporting GPRS and any other network are involved in the execution of a GPRS service request.
The GPRS standard supports several quality of service profiles as well as a variety of mobile station (MS) operational modes. For example an MS operating in A mode of operation performs GPRS and other GSM services simultaneously, an MS in B mode of operation simultaneously monitors GPRS and other GSM service control channels, but only performs one set of services at one time, and a MS in C mode of operation only performs GPRS services.
Generally, to initially access GPRS services, an MS must attach to a GPRS network and establish a logical link between the MS and the Serving GPRS Support Node (SGSN) of the GPRS network. The SGSN is described in more detail in the detailed description of the invention. The MS must also activate the packet data address to send and receive GPRS data over the GPRS network, this operation announces the MS to a corresponding Gateway GPRS Support Node (GGSN) so that interworking with external data networks can commence. The GGSN is also described in more detail in the detailed description of the invention.
User data is transferred between the MS and the external data networks by a method known as encapsulation and tunnelling, whereby data packets are equipped with GPRS-specific protocol information and transferred between the MS and GGSN. This transfer method has the advantage that it lessens the requirement for the GPRS network to interpret external data protocols.
The general problem in implementing the GPRS network infrastructure with the existing GSM system architecture to include multi-beam geostationary satellite systems is that no system exists for the efficient transfer of packet data between networks in separate countries.
In general, efficiency of such a data network increases as the amount of data interpretation and the steps involved in data transfer decrease. A general measure of this efficiency is cost. Cost can be used as an indication of the efficiency of the paths that data packets are routed. As cost decreases, efficiency generally increases. The present invention describes a network and system whereby cost may be substantially reduced as compared with known terrestrial networks. In order to minimize the cost of transferring data packets to/from an MS employing a Satellite GPRS network, some times data packets must be transferred between networks in separate countries. A problem occurs in that the current GPRS systems do not specifically allow for the determination of a “least cost routing” between such networks in different countries. The cost minimization problem exists for both downlink (mobile terminated) and uplink (mobile originated) packet data transferred from and to the external packet data networks (PDNs), X.25 and IP networks. The present disclosure particularly addresses this problem for packet transfer to/from IP networks.
In the case of internetworking with IP networks, the entire satellite GPRS network will be defined as one Autonomous System (AS). The Internet is composed of multiple ASs. It is assumed that Border Gateway Protocol (BGP) [IETF RFC 1771] is used as an Exterior Gateway Protocol (EGP) between ASs whereas Open Shortest Path First (OSPF) [IETF RFC 2328] is used as an Interior Gateway Protocol (IGP) inside each AS. Usage of other EGPs or IGPs may be applicable, and the present invention is not limited to these specific examples.
To support the delivery of packets to hosts within the GPRS AS, the GGSNs must broadcast to the other ASs the addresses of hosts reachable through them. As the GPRS system is assumed to be one AS, the GGSNs will advertise the same path attribute in their BGP route update messages for reaching the MSs attached to the Satellite GPRS system. Therefore, any GGSN, given that it has an agreement with a particular ISP, can act as a gateway to the Internet for an MS independent of the MS's physical location. This may lead to the situation where packets destined for an MS may not use the country's GPRS network that the MS is attached to as the entry gateway for packets coming from the Internet. This will create across country traffic in the GPRS system.
The problem may also occur for uplink data transfer. Following the standard GPRS procedures, an MS registered with an SGSN will have to create a PDP context before packets can actually be transferred in the uplink direction. The context may be activated with any GGSN. If the chosen GGSN is in another country, this will again create across country packet data transfer. If the GGSN is in the same country with the SGSN, packets from the MS will have to be routed through that country's GPRS network regardless of the other end of the communication path. With the routing dynamics in the Internet and inside the GPRS AS, routing inside the GPRS AS may change and packet transfer between different countries' GPRS networks may be required, leading again to across country data traffic.
Therefore, independent of the direction of the packet flow during the actual transfer, if across country packet data transfer occurs “too often,” as explained in the detailed description of the invention, this will create an inefficient packet data routing and produce the least cost routing problem.
The present invention dynamically achieves least cost routing for a mobile station in a satellite GPRS system, thereby minimizing the least cost routing problem, based on the real-time behavior of IP data packets while necessitating minimal new requirements to the existing terrestrial GPRS network infrastructure.